<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>level 2</title>
</head>
<body>
level 2
请输 入答案：
<input type="text" id="in"><button onclick="check()">提交</button>
<script>
    function check(){
        var ui=document.getElementById('in').value;
        if(ui=='入答案')window.open("l3.html");
        else alert('错误');
    }
</script>
</body>
</html>